Evolution of Papanicolaou Staining in Cervical Cytology: From Conventional Smears to Liquid-Based and Digital Cytopathology - A Narrative Review

Background

Papanicolaou staining remains central to cervical cytology, but its laboratory context has expanded from conventional smears to liquid-based preparation, automated screening, digital cytopathology, molecular testing, and artificial intelligence. Objective of the review: To critically synthesize the evolution of Papanicolaou staining and cervical cytology, with emphasis on staining principles, conventional and liquid-based methods, quality assurance, automation, digital imaging, HPV-based triage, artificial intelligence, workflow, and implementation challenges. Key findings: Conventional smears are inexpensive and information-rich but remain vulnerable to sampling, fixation, transfer, and screening variability. Liquid-based cytology improves preparation standardization and facilitates residual-sample molecular testing, although diagnostic advantage is setting- and platform-dependent. Automation can improve reproducibility and throughput, whereas digital cytopathology enables remote review and computational analysis but introduces scanning, storage, validation, and governance requirements. Artificial intelligence may support prioritization, quality control, and classification, but dataset shift, external validation, and human oversight remain critical.